U.S. patent number 7,305,889 [Application Number 11/495,318] was granted by the patent office on 2007-12-11 for microelectromechanical system pressure sensor and method for making and using.
This patent grant is currently assigned to General Electric Company. Invention is credited to Jeffrey Fortin, Kuna Kishore, Kanakasabapathi Subramanian.
United States Patent |
7,305,889 |
Fortin , et al. |
December 11, 2007 |
Microelectromechanical system pressure sensor and method for making
and using
Abstract
According to some embodiments, an apparatus includes a substrate
that defines a plane. The apparatus also includes a first
conducting plate that is substantially normal to the substrate and
a second conducting plate that is (i) substantially normal to the
substrate and (ii) deformable in response to a pressure.
Inventors: |
Fortin; Jeffrey (Niskayuna,
NY), Kishore; Kuna (Bangalore, IN), Subramanian;
Kanakasabapathi (Albany, NY) |
Assignee: |
General Electric Company
(Niskayuna, NY)
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Family
ID: |
34827671 |
Appl.
No.: |
11/495,318 |
Filed: |
July 31, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060260411 A1 |
Nov 23, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10799053 |
Mar 12, 2004 |
7114397 |
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Current U.S.
Class: |
73/756 |
Current CPC
Class: |
G01L
1/148 (20130101); G01L 9/0073 (20130101) |
Current International
Class: |
H04R
17/00 (20060101) |
Field of
Search: |
;73/753
;361/283.1,283.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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4223616 |
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Jul 1992 |
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DE |
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1353161 |
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Oct 2002 |
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EP |
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Other References
EP Search Report Oct. 18, 2005. cited by other .
J.-S. Park and Y.B. Gianchandani, "A Low Cost Batch-Sealed
Capacitive Pressure Sensor," IEEE No. 0-7803-5194-0 (1999). cited
by other .
A. V. Chavan and K. D. Wise, "A Monolithic Fully-Integrated
Vacuum-Sealed CMOS Pressure Sensor," IEEE No. 0-7803-5273-4 (2000).
cited by other .
Wen H. Ko and Qiang Wang, "Touch Mode Capacitive Pressure Sensors
For Industrial Applications," IEEE No. 0-7803-3744-1 (1997). cited
by other .
Hyeoncheol Kim and Kukjin Chun, "Integrated MEMS for Pressure
Transponder," 1997 International Conference on Solid-State Sensors
and Actuators, IEEE No. 0-7803-3829-4 (1997). cited by other .
W. P. Eaton and J. H. Smith, "Micromachined Pressure Sensors:
Review and Recent Developments," Smart Mater. Struct. 6, p. 530-539
(1997). cited by other .
Abhijeet V. Chavan and Kensall D. Wise, "A Monolithic
Fully-Integrated Vacuum-Sealed CMOS Pressure Sensor," IEEE
Transactions on Electron Devices, vol. 49, No. 1 (Jan. 2002). cited
by other .
C. Hierold et al., "Implantable Low Power Integrated Pressure
Sensor System for Minimal Invasive Telemetric Patient Monitoring,"
IEEE No. 0-7803-4412-X (1999). cited by other.
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Primary Examiner: Allen; Andre J.
Attorney, Agent or Firm: Powell, III; William E. Brueske;
Curtis B.
Parent Case Text
The present patent application is a divisional application from
U.S. patent application Ser. No. 10/799,053, filed Mar. 12, 2004
now U.S. Pat. No. 7,114,397, the disclosure of which is hereby
incorporated by reference in its entirety.
Claims
What is claimed:
1. A method, comprising: on a wafer that includes a first
non-conducting layer bonded onto a conducting layer, etching
substantially parallel trenches through the layers to form a
plurality of conducting plates substantially normal to a plane
defined by the wafer, wherein at least one conducting plate is to
be deformable in response to pressure; and bonding a second
non-conducting layer onto the first non-conducting layer.
2. The method of claim 1, wherein pairs of conducting plates form
fingers.
3. The method of claim 2, wherein a first set of fingers is formed
on a first comb and a second set of fingers is formed on a second
comb, the fingers of the first and second combs being
interleaved.
4. The method of claim 3, further comprising: etching away a
portion of the second non-conducting layer and the first
non-conducting layer to expose a portion of the conducting
layer.
5. The method of claim 4, further comprising: creating a vacuum
within a finger.
6. The method of claim 4, further comprising: bonding a cap wafer
onto the second non-conducting layer.
7. The method of claim 6, wherein the cap wafer includes at least
one of: (i) a ground via, (ii) a voltage via, (iii) a first
pressure via, and (iv) a second pressure via.
8. The method of claim 1, wherein at least one pressure input
cavity is formed while etching the trenches.
Description
BACKGROUND
A pressure sensor may convert an amount of pressure into an
electrical value. For example, a pressure sensor may use a sensor
diaphragm or membrane positioned parallel to a plane of a wafer to
convert an amount of pressure into a capacitance value. Note that
the overall size of the pressure sensor may be important. For
example, the amount of space on a wafer that is occupied by a
pressure sensor (referred to as the sensor's "footprint") might
make a device expensive to produce and/or make the sensor
impractical for some applications. Thus, it may be important that a
pressure sensor does not occupy too large of an area on a
wafer.
In addition, increasing the sensitivity of a pressure sensor might
require an increase in the sensor's footprint. Moreover, such a
change could require that some parts of the sensor are completely
re-designed (which can be a difficult and time-consuming
process).
SUMMARY
According to some embodiments, an apparatus includes a substrate
that defines a plane. The apparatus also includes a first
conducting plate that is substantially normal to the substrate and
a second conducting plate that is (i) substantially normal to the
substrate and (ii) deformable in response to a pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a known pressure sensor.
FIG. 2 is a side view of the pressure sensor of FIG. 1.
FIG. 3 is a perspective view of an apparatus constructed in
accordance with an exemplary embodiment of the invention.
FIG. 4 is a side view of the apparatus of FIG. 3.
FIG. 5 is a cross-sectional view of a sealed pressure sensor
constructed in accordance with an exemplary embodiment of the
invention.
FIG. 6 is a perspective view of the sealed pressure sensor of FIG.
5.
FIG. 7 is a side view of an apparatus constructed in accordance
with another exemplary embodiment of the invention.
FIG. 8 is a top view of a pressure sensor with a vertical capacitor
array constructed in accordance with another exemplary embodiment
of the invention.
FIG. 9 is a side view of the pressure sensor of FIG. 8.
FIG. 10 illustrates a method to measure pressure according to some
embodiments.
FIG. 11 illustrates a method to create a pressure sensor according
to some embodiments.
FIG. 12 is a perspective view of a wafer constructed in accordance
with another exemplary embodiment of the invention.
FIG. 13 is a top view of the wafer of FIG. 12 after trenches have
been etched.
FIG. 14 is side view of the wafer of FIG. 13.
FIG. 15 is side view of the wafer of FIG. 14 after another
non-conducting layer has been added.
FIG. 16 is a side view of a wafer of FIG. 15 after a portion of the
top non-conducting layer has been removed.
FIG. 17 is a differential pressure sensor constructed in accordance
with another exemplary embodiment of the invention.
FIG. 18 is a system constructed in accordance with another
exemplary embodiment of the invention.
FIG. 19 is a piezoresistance pressure sensor constructed in
accordance with another exemplary embodiment of the invention.
FIG. 20 is a top view of a bare die after deep trenches have been
etched according to an exemplary embodiment of the invention.
FIG. 21 is a top view of the die of FIG. 20 after an oxide cap has
been placed on the die and portions of the oxide cap have been
etched away according to an exemplary embodiment of the
invention.
FIG. 22 is a perspective view of a cap wafer that might be used in
connection with the die of FIG. 21 according to an exemplary
embodiment of the invention.
FIG. 23 is a perspective view of a pressure sensor according to an
exemplary embodiment of the invention.
DETAILED DESCRIPTION
FIG. 1 illustrates a capacitive pressure sensor 100. The sensor 100
includes a pair of conducting plates 110, 120 that are positioned
substantially parallel to a horizontal plane that is defined by a
non-conducting substrate 130 (e.g., a wafer). Note that in some
cases, the plate 110 could formed as an integral part of the
substrate 130. One of these plates 120 is deformable in response to
pressure (P). In particular, as shown in the side view of the
sensor 100 illustrated in FIG. 2, the plate 120 might be a thin
film diaphragm that flexes such that the distance between the two
plates 110, 120 will decrease when a pressure P acting on the
conducting plates 110, 120 is increased.
Note that the capacitance C between the plates 110, 120 depends in
part on the distance between them. In particular, when the two
plates 110, 120 are electrically isolated from each other, it can
be detected that the amount of capacitance C increases as the
plates 110, 120 move together. An increase in the pressure P,
therefore, can be measured based on the increased capacitance C,
since the increased pressure will push one plate 120 closer to the
other plate 110. Instead of capacitance, a resistance associated
with a single deformable plate or diaphragm might be used to
measure pressure. For example, one or more piezoreistors could be
embedded in a diaphragm. In this case, the diaphragm itself might
be formed of a non-conducting material.
The plates 110, 120 used for the pressure sensor 100 sensor might
be, for example, several hundred microns wide. Moreover, improving
the sensitivity of the sensor 100 may require even larger plates
110, 120. The relatively large footprint associated with the sensor
100 might make the device expensive to produce and/or make the
sensor 100 impractical for some applications. In addition, the
large plates 110, 120 could be damaged if too much pressure is
applied (e.g., the flexible plate 120 could detach from a
supporting structure).
FIG. 3 is a diagram of an apparatus 300 according to some
embodiments. The apparatus 300 may be, for example, a
Microelectromechanical System (MEMS) device.
As before, a first conducting plate 310 and a second conducting
plate 320 are provided on a non-conducting substrate 330. The
plates 310, 320 may be formed, for example, using silicon and the
substrate may formed using oxide. As illustrated, the plates 310,
320 are substantially normal to the substrate 330. That is, the
plates 310, 320 extend vertically from a horizontal plane defined
by the substrate 330.
At least one of the plates 310, 320 is deformable in response to a
pressure P. The deformable plate may, for example, flex in a
direction substantially in the horizontal plane. Referring to the
side view of the apparatus 300 illustrated in FIG. 4, the second
plate 320 may flex such that the distance between the two plates
310, 320 will decrease when the pressure P is increased. Thus, when
the two plates 310, 320 are electrically isolated from each other,
it can be detected that the capacitance C increases as the pressure
P increases. Because the plates 310, 320 extend vertically from the
substrate 330, the footprint of the apparatus 300 might be, for
example, a few microns in width.
FIG. 5 is a cross-sectional view of a sealed pressure sensor 500
according to some embodiments. A first conducting plate 510 and a
second conducting plate 520 extend vertically from a horizontal
plane defined by a substrate 530. Note that, as illustrated, both
plates 510, 520 are deformable in response to pressure. This
capability increases the change in capacitance, and therefore,
improves the sensitivity of the sensor 500. A cap 540 has been
provided at an end of the plates 510, 520 opposite from the
substrate 530. FIG. 6 is a perspective view of the sensor 500
including the substrate 530 and cap 540. A back wall 550 and a
front wall 560 (which is shown apart from the sensor 500 in FIG. 6
only for the purpose of illustration) are also provided so that a
vacuum (V) can be created in the chamber between the two conducting
plates 510, 250 (this may also improve the sensitivity of the
sensor 500). With respect to the embodiment illustrated in FIGS. 5
and 6, the cap 540 may be formed using a non-conducting material so
that the plates are electrically isolated from each other. Note a
reference pressure other than a vacuum might be provided in the
chamber between the two conducting plates 510, 520. In this case,
the side walls of the chamber may deflect inward. That is, the
center of the side walls might flex toward the vacuum while the
four edges of each side wall remain fixed.
FIG. 7 is a side view of an apparatus 700 according to other
embodiments. In this case, two pairs of conducting plates are
provided, each pair enclosing a vacuum V therebetween. As used
herein, the term "finger" will refer to such a pair of conducting
plates (with or without a vacuum). Note that, in this embodiment,
two plates within a finger may be electrically coupled to each
other.
According to this embodiment, the first finger 710 is electrically
isolated from the second finger 720. When the ambient pressure
increases, the plates on the fingers 710, 720 deform inward. Thus,
the capacitance C between one plate of the first finger and another
plate of the second finger decreases. An imbalance between the
ambient pressure and the pressure between the plates of each finger
causes the plates of each finger to bow inwardly and thus away from
the nearest plate of the adjacent finger, thereby causing the
decrease in the capacitance C.
In this way, the capacitance C can be used to sense pressure (e.g.,
with an increase in C representing a decrease in P). Note that, in
this embodiment, air acts as the dielectric of the capacitor
(unlike FIG. 2, where the vacuum acted as the dielectric). As a
result, a change in temperature and/or humidity may also result in
a change in the capacitance C. Therefore, in some applications a
separate temperature and/or humidity sensor may be provided to
account for this effect. Also note that any technique might be used
to measure an amount of and/or a change in the capacitance C. For
example, a change in capacitance might be converted into a voltage
that can be measured and/or approaches using Alternating Current
(AC) could be implemented.
FIG. 8 is a top view of a pressure sensor 800 with a vertical
capacitor array according to some embodiments. In particular, the
sensor 800 includes a first comb 810 with a conducting base and
three fingers that extend away from the base (as well as vertically
from a substrate not illustrated in FIG. 8). The sensor 800 also
has a second comb 820 with a conducting base and three fingers. The
combs 810, 820 are positioned such that the fingers of one are
interleaved with the fingers of the other. Note that although each
comb 810, 820 illustrated in FIG. 8 has three fingers, any number
of fingers may be provided.
The first comb 810 is electrically isolated from the second comb
820. Note that when the ambient pressure increases, the plates on
all of the fingers will deform inwardly. Thus, the capacitance C
between the fingers will decrease (e.g., because neighboring plates
are pushed further apart). Also note that the five capacitance
values C associated with this embodiment are connected in parallel.
Therefore, the values will add to each other, improving the
pressure sensitivity of the sensor 800.
FIG. 9 is a side view of the pressure sensor 800 according to this
embodiment. Note that the combs may be provided on a non-conducting
layer 920 (e.g., such that the two combs are electrically isolated
from each other). Moreover, the non-conducting layer 920 may be
bonded to another layer 910 to provide structural support.
According to some embodiments, this supporting layer 910 is a glass
wafer (e.g., to reduce parasitic capacitance effects). The support
layer 910 could also be a lightly doped or intrinsic silicon wafer.
Note that the characteristics of the pressure sensor 800 may depend
in part on the geometry of the elements, such as the thickness
height, and length of the plates as well as the gap between
neighboring plates. By way of example only, the thickness of a
conducting plate might be from 2 to 15 micrometers (.mu.m), the
height of a conducting plate might be from 100 to 500 .mu.m, the
gap between conducting plates might be from 2 to 20 .mu.m, and the
length of a conducting plate might be 1000 .mu.m. The appropriate
dimensions for a particular sensor might depend on, for example,
the applications for which that sensor will be used.
Thus, some embodiments provide a sensor that is sensitive to
changes in pressure while occupying a relatively small area since
the sensor is disposed in a vertical relationship to the wafer
surface. Such an approach may provide a MEMS sensor that is
scalable and inexpensive to produce (e.g., because new fingers may
be added without any change in the fabrication process and with
only a small increase in the sensor's footprint). Moreover, new
pressure sensors may be easy to design by adding fingers as
appropriate, and be less likely to be damaged.
FIG. 10 is a flow chart of a method to measure pressure according
to some embodiments. a voltage is provided to one of a first
conducting plate and a second conducting plate, the first
conducting plate being substantially normal to a substrate defining
a plane and the second conducting plate being (i) electrically
isolated from the first conducting plate, (ii) substantially normal
to the substrate, and (iii) deformable in response to pressure. The
first conducting plate may be, for example, associated with a
finger of a first comb while the second conducting plate is
associated with a finger of a second comb that is electrically
isolated from the first comb.
At Step 1004, pressure is measured based at least in part on an
amount of capacitance that is detected between the two plates. For
example, a decrease in capacitance may indicate an increase in the
absolute atmospheric pressure.
FIG. 11 is flow chart of a method to create a pressure sensor
according to some embodiments. Note that the actions described with
respect to FIG. 11 may be performed in any order that is practical.
At Step 1102, a substrate of conducting silicon is provided. In
some cases, a backing wafer is bonded to the substrate at Step 1104
to provide additional support.
At Step 1106, vertical trenches are etched into the substrate using
an appropriate etch mask. The etch mask may, for example, comprise
a layer in which a pattern of oxide defines areas that will not be
etched.
According to some embodiments, a capping substrate is bonded to the
etched structure at Step 1108. Note that in this embodiment, the
etched substrate and the capping substrate might not need to be
electrically isolated from each other. At Step 1110, a vacuum or
other pressure level is created in a cavity formed by the etched
structure and capping substrate. At Step 1112, the capping
substrate is etched as appropriate to create isolated figures with
caps. If desired, a cap wafer may then be attached at Step 1114 to
provide pressure and electrical feed-throughs or vias.
According to another embodiment, after the vertical trenches are
etched in the substrate at Step 1106, a capping structure or wafer
with an insulating layer is bonded to the etched structure at Step
1116. That is, the capping wafer may be electrically isolated from
the etched structure. At Step 1118, a vacuum or other pressure
level is created in a cavity formed by the etched structure and the
capping wafer. At Step 1120, the capping wafer is patterned as
appropriate to provide pressure and electrical feed-throughs or
vias.
By way of example, consider the wafer 1200 illustrated in FIG. 12.
The wafer 1200 may include a base layer 1210 of non-conducting
material, such as an oxide layer. In some embodiments, the base
layer 1210 is bonded onto a backing wafer 1240, such as a layer of
glass (or lightly doped silicon), that provides structural support
for the wafer 1200.
A conducting layer 1220 is provided on the base layer 1210. The
conducting layer 1220 may be, for example, a layer of highly-doped,
single-crystal silicon. An etch mask layer 1230 (e.g., oxide) is
then deposited on layer 1220 and patterned . . . Note that the
materials used to form these (and other) layers described herein
might be selected based at least in part on thermal coefficients of
expansion (e.g., to ensure that a device will operate correctly
over a range of temperatures). Materials might also be selected in
accordance with conductivity characteristics (e.g., to insure that
device electrodes remain electrically isolated from each
other).
The etch mask layer 1230 may then be used to etch substantially
parallel trenches through the conducting layer 1220. FIG. 13 is a
top view of the wafer 1200 after the trenches have been etched
(with the cross-hatched areas representing the trenches) according
to some embodiments. The trenches define a series of substantially
parallel, conducting plates. Moreover, the plates are substantially
vertical to a horizontal plane defined by the wafer 1200, and at
least one of the plates is deformable in response to pressure. Note
that pairs of plates, or fingers 1330, are formed for both a first
comb 1310 and a second comb 1320. According to some embodiments, at
least one pressure input cavity is also formed while the trenches
are etched. FIG. 14 is side view of the wafer 1200 after trenches
have been etched according to some embodiments.
An additional non-conducting layer may then be bonded onto the
wafer. FIG. 15 is side view of the wafer 1200 after the
non-conducting layer 1250 has been added according to some
embodiments. This non-conducting layer 1250 may be an oxide capping
structure. Note that vacuums V may now be provided between pairs of
vertical plates. For example, some or all of the steps described
herein might be performed within a vacuum to create the vacuums
V.
A portion of the additional non-conducting layer 1250 may then be
etched away. One potential etching material may include potassium
hydroxide. For example, FIG. 16 is a side view of the wafer 1200
after a portion of the top non-conducting layer has been removed
according to some embodiments. In particular, the non-conducting
layer 1250 now includes caps over pairs of plates that were formed
in the conducting layer 1220, resulting a number of sealed fingers
1260.
According to some embodiments, a cap wafer is bonded onto the
additional non-conducting layer 1250. The cap wafer may include,
for example, a ground via (e.g., a hole through which a ground wire
may be routed to allow some fingers to be held at a ground voltage
level), a voltage via (e.g., to allow some fingers to be at voltage
level other than ground), and/or pressure vias.
The following illustrates various additional embodiments of the
present invention. These do not constitute a definition of all
possible embodiments, and those skilled in the art will understand
that the present invention is applicable to many other embodiments.
Further, although the following embodiments are briefly described
for clarity, those skilled in the art will understand how to make
any changes, if necessary, to the above-described apparatus and
methods to accommodate these and other embodiments and
applications.
Some embodiments have been described herein with respect to an
absolute pressure sensor, but embodiments may be used in connection
with a gauge or differential pressure sensor. For example, FIG. 17
is a differential pressure sensor 1700 according to some
embodiments. As before, some fingers are deformable in response to
a first pressure P1. In this case, however, channels are provided
so that some or all of the fingers are deformable in response to a
second pressure P2. As a result, a change in capacitance may be
associated with a difference between the first and second
pressures. Note that the vias through the substrate for electrical
and pressure connection may be located in either the backing
substrate 1740 or a capping substrate.
While embodiments have been described with respect to pressure
sensors, note that any of the embodiments may be associated with a
system that uses a pressure sensor. For example, FIG. 18 is a
system 1800 according to some embodiments. The system 1800 includes
a MEMS pressure sensor 1810 that operates in accordance with any of
the embodiments described herein. For example, the MEMS pressure
sensor 1810 might include a substrate that defines a horizontal
plane, a first conducting plate substantially vertical to the
substrate, and a second conducting plate substantially vertical to
the substrate and deformable in response to a pressure (P).
Information from the MEMS pressure sensor 1810 is provided to a
pressure dependent device 1820 (e.g., via an electrical signal).
The pressure dependent device 1820 might be, for example,
associated with a pressure display, an engine or automotive device
(e.g., a tire pressure monitor), an ultrasonic transducer, a
medical device (e.g., a blood pressure sensor), and/or a
barometer.
In addition, although some embodiments have been described with
respect to the use of a capacitance value to sense an amount of
pressure, embodiments might be associated with other types of
displacement sensing techniques. FIG. 19 is a pressure sensor 1900
constructed in accordance with another exemplary embodiment of the
invention. In this case, a plate 1910 or diaphragm is provided on a
substrate 1920. As illustrated, the plate 1910 extend vertically
from a horizontal plane defined by the substrate 1920. Moreover,
the plate 1910 is deformable in response to a pressure P. The
deformable plate 1910 may, for example, flex in a direction
substantially in the horizontal plane. According to this
embodiment, an amount of resistance R associated with the plate
1910 varies depending on an amount of stress (e.g., a portion of
the plate 1910 may have piezoelectric and/or piezoresistance
characteristics or devices having such characteristics may be
embedded into or onto the plate 1910). As a result, the resistance
R may be measured and used to determine a corresponding amount of
pressure P. Because the plate 1910 extends vertically from the
substrate 1920, the footprint of the sensor 1900 may be reduced as
compared to traditional devices (e.g., having a diaphragm
positioned horizontal to the substrate 1920). Note that according
to this embodiment, the substrate 1920 may or may not be
conductive. Also note that the sensor 1900 may be constructed using
any of the techniques described herein (e.g., by etching trenches
into a substrate).
In addition, although particular layouts and manufacturing
techniques have been described herein, embodiments may be
associated with other layouts and/or manufacturing techniques. For
example, FIG. 20 is a top view of a die 2000 according to an
exemplary embodiment of the invention. In particular, trenches have
been etched into the die 2000 to create a chamber 2030 that opens
into the cavities of a number of fingers 2040 associated with a
first comb 2020. Similarly, another chamber 2032 opens into
cavities of fingers 2042 associated with a second comb 2022. A wall
2010 surrounding the two combs 2020, 2022 may be provided so that a
cap can be bonded to the die 2000. Note that all of the etching
illustrated in FIG. 20 might be performed during a single process
step.
FIG. 21 is a top view of the die of FIG. 20 after an oxide cap has
been placed on the die and portions of the oxide cap have been
etched away according to an exemplary embodiment of the invention.
The remaining portion of the layer of oxide 2100 is illustrated by
cross-hatching. The oxide layer 2100 may include windows through
which pressure can reach the chambers 2030, 2032 and, eventually,
the otherwise sealed cavities of the fingers.
FIG. 22 is a perspective view of a cap wafer 2200 that might be
used in connection with the die of FIG. 21 according to an
exemplary embodiment of the invention. The cap wafer 2200 includes
five via through which internal portions of the sensor can be
reached. In particular, one via is provided for a first pressure P1
and two vias are provided for a second pressure P2. Moreover, two
electrical vias 2202 may associated with opposite sides of a
capacitor.
FIG. 23 is a perspective view of a pressure sensor package 2300
according to an exemplary embodiment of the invention. In
particular, the cap wafer 2200 has been bonded onto the oxide layer
2100. The cap wafer 2200 might be oriented, for example, such that
the via associated with pressure P2 are aligned with the chambers
2030, 2032. A bottom cap 2310 might also be provided for the
package 2300. Pressure ports and electrical ports may be
individually interchangeable between front and back side.
The present invention has been described in terms of several
embodiments solely for the purpose of illustration. Persons skilled
in the art will recognize from this description that the invention
is not limited to the embodiments described, but may be practiced
with modifications and alterations limited only by the spirit and
scope of the appended claims.
* * * * *